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Hippos of the Black Volta River Print E-mail




Don't be scared. I'm Nicky Green and I'll protect you from the hippos.

3. Estimating the Hippopotamus Population in Bui National Park
Daniel Bennett, Dept. Zoology, University of Aberdeen, Scotland.

The hippo (Hippopotamus amphibius) is considered widespread and secure by the IUCN (Eltringham in Oliver 1993). However populations in West Africa have been in decline for at least a hundred years and only 7,000 animals are thought to be left in the entire subcontinent, compared with 150,000 animals in Eastern and Southern Africa. In Ghana the hippo is classed as endangered and is afforded complete protection under national law. It was once widespread throughout the Volta system but the only surviving animals are found in the Black Volta River from Bui National Park upstream to the border with Burkina Faso. Within this area two populations have been identified, one within Bui National Park and another around Wichan, near Wa in the north of the country. Neither population is well defined and only in the former area is the hippos' habitat afforded protection.

The aim of this study was to make an estimate of the hippopotamus population within Bui National Park and to investigate interactions between hippos and people in the area. The work was conducted by members of the Aberdeen University Black Volta '97 Expedition between June and July 1997.

Proposed methodology assumed;

1. That hippos would be in the water during the day and out of the water during the night.

2. That individual animals could be identified and subsequently recognised by taking photographs of the creases around the eye with a 600mm lens, having been enticed to lift their heads above the water using the mirror technique described by Kardstad & Hudson (1984) and Norton (1988).

3. That it would be possible to survey the entire length of the Black Volta River within Bui National Park during the study.

In practice, none of these assumptions were valid. Heavy rains just prior to our visit caused the level of the river to rise and much of the riverine forest was flooded. As a result the river was twice as wide as had been expected and access to the riverbank was impossible except in a few places. Cloud cover prevented the use of the mirror technique, and the 600mm lens used to photograph individual hippos did not provide sufficient magnification to reveal eye creases. Subsequent investigations revealed that the movement patterns of individual hippos could not be predicted from the time of day, with animals found in the water at all hours of the night, and on the riverbank at most times of the day. Finally, the flooded condition of the forest and the swollen tributaries made walking along the river course very slow and precluded studies in central and northern sectors of the river. On the recommendation of Ghana Wildlife Department the aims of the hippo survey were altered to make an estimate of hippo numbers in the southern portion of Bui National Park, from Batoo village upstream as far as Bope, which includes a large part of the area that will be affected by the Bui Dam (Map 1). Traditional local canoes were used for the survey, each containing two local fishermen and two expedition members. Areas of the river were surveyed daily (except Sundays) throughout July. Estimates were made by recording numbers of heads visible every 15 seconds for at least five minutes, and using the maximum value obtained. Usually fishermen’s’ estimates of total numbers were higher than those of researchers, but the lower value was used. Sexes were assigned on an arbitrary basis with the largest animals classified as males and smaller adults as females. Babies were easy to identify by their very small size. Juveniles were animals other than babies whose size suggested they had not reached sexual maturity. In addition some groups were seen from the riverbank.



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